1. Field of the Invention
The present invention relates to a sensor module for detecting a relative displacement of an object and more particularly, to a sensor module for detecting a relative displacement of a cylindrical actuator in a non-contact manner using a Giant Magneto Resistance (GMR) sensor.
2. Discussion of the Related Art
Generally, a cylindrical actuator which is operated by hydraulic or pneumatic pressure is widely used in a vehicle or an industrial equipment and the cylindrical actuator includes a cylinder, a piston valve which reciprocates inside the cylinder and a piston rod connected to the piston valve to transmit a driving force, etc.
In addition, in a case of controlling precisely an operation of an actuator or in a case that automatization of the actuator is requested, the operation of an actuator is controlled by detecting a displacement of the piston valve or a piston using a sensor and feed-backing the detection result.
For example, a damper, which constructs a cylindrical actuator used in a vehicle, is installed between a vehicle body and a wheel of the vehicle to serve to absorb vibration or impact from the road surface, and an electronically controlled damper installed in a luxury car detects a relative position of an axle and a vehicle body through a sensor and controls actively its damping force or tensile force.
Therefore, a sensor which is detectable of a state of an actuator should be used in order to feedback-control the operation of the electronically controlled damper or other cylindrical actuator. Various kinds of sensors are currently used and the sensors can be largely divided into a contact sensor and non-contact sensor.
However, because the contact sensor (for example, a potentiometer) detects a moving state of a piston rod or a piston valve in a state of contacting with the piston rod or the piston valve, there are problems that the sensor is frequently damaged due to a friction and has a relatively short product life.
In addition, there is an optical sensor as a typical non-contacting sensor and it has problems that it is weak in an impact and cannot be used when light is blocked by a foreign body.